1. Technical Field
The present invention relates to a controller of a mobile robot which performs an operation of holding an object, such as a cart, with hands at distal portions of arms thereof, and moving the object such that the position and the posture of the object follow desired trajectories.
2. Description of the Related Art
A technique for having a mobile robot perform an operation of moving an object, such as a cart, with the distal portions of the arms of the mobile robot kept in contact with predetermined portions at one end of the object has been proposed by the present applicant as disclosed in, for example, Japanese Patent Application Laid-Open No. 2007-160428 (hereinafter referred to as patent document 1). According to the technique, the motions of a bipedal mobile robot as the mobile robot are controlled such that the position of a representative point of the object and the posture of the object follow a desired position trajectory and a desired posture trajectory, respectively, based on a movement scheme of the object.
However, in this type of conventional technique, the representative point of the object which should follow the desired position trajectory of the object is set fixedly with respect to the object. This has been presenting the following inconvenience.
For example, as is shown in FIGS. 5(a) and (b), a case is assumed where a robot 101 pushes and moves a cart 200 in the state of the robot 101 holding a handle 201 at one end of the cart 200 as an object by distal portions (hands) of arms 102, 102. FIGS. 5(a) and (b) are plan views illustrating the robot 101 and the cart 200 observed from above, at one point in time during movement of the robot 101 and the cart 200.
It is assumed that a spatial desired route 203 defined by the desired position trajectory of a representative point 202 of the cart 200 is curved at a relatively large degree of curve, at the front of the current traveling direction of the robot 101 and the cart 200. Further, it is assumed that a desired posture of the cart 200 on the desired route 203 (the desired posture of the cart 200 observed in the yaw axis direction) is a posture in which the longitudinal direction of the cart 200 is in the tangential direction of the desired route 203 (same direction as a direction of a moving velocity vector of the representative point 202 of the cart 200 on the desired route 203). The “yaw axis” means an axis in the direction perpendicular to a floor surface in an environment in which a mobile robot 101 and the cart 200 move or an axis in the vertical direction.
In such case, the robot 101 tries to make the posture of the cart 200 follow the desired posture (posture of the cart 200 indicated by two-dot chain line in FIGS. 5(a) and (b)), by making the cart 200 rotate about the yaw axis taking the representative point 202 as a supporting point, while making the representative point 202 of the cart 200 follow the desired position on the desired route 203.
In the case where the representative point 202 of the cart 200 is set to the end on the robot 101 side, as is shown in FIG. 5(a), the amount of movement of the portion away from the representative point 202 of the cart 200 (end on the other side from the end on the robot 101 side) about the yaw axis becomes large. Therefore, in the case where obstacles exist at the side of the desired route, such as when the cart 200 is moved in a relatively narrow pathway, there is a fear that collision occurs between the cart 200 and the obstacles. Further, the moment of inertia of the cart 200 about the yaw axis passing the representative point 202 is relatively large. Therefore, although the stability of the posture of the cart 200 with respect to variation in the force acting on the cart 200 from the robot 101 is high, it is difficult to make the posture of the cart 200 follow the desired posture in a short time with respect to the sudden change in the desired posture of the cart 200. In such case, the actual moving route and the desired route of the cart 200 tends to deviate from the influence of the restriction in the position-posture relationship between the robot 101 and the cart 200, and the like.
On the other hand, as is shown in FIG. 5(b), in the case where the representative point 202 of the cart 200 is set to a position away from the robot 101 towards the end on the other side from the end on the robot 101 side (in the illustrated example, approximately at the middle position of the cart 200), the amount of movement of the portion away from the representative point 202 of the cart 200 when making the posture of the cart 200 change towards the desired posture becomes smaller than in the case shown in FIG. 5(a). Further, the moment of inertia of the cart 200 about the yaw axis passing the representative point 202 is smaller than in the case shown in FIG. 5(a).
In this case, however, because the moment of inertia of the cart 200 is small, the posture of the cart 200 tends to change from small variation in the force acting on the cart 200 from the robot 101, even in the case where the desired posture of the object is made constant and the object is made to move linearly. Further, in the case where the posture of the cart 200 deviates with respect to the desired posture from the influence of the variation in the force acting on the cart 200 from the robot 101 or from a disturbance, it is frequently the case where the robot 101 must move in the lateral direction with respect to the desired route 203 (direction approximately orthogonal to the desired route 203), in order to resolve the deviation of the posture of the cart 200 while maintaining an appropriate position-posture relationship between the robot 101 and the cart 200. Therefore, it is frequently the case where the robot 101 must move in the lateral direction even if the desired route 203 is an approximately linear route. Consequently, it becomes difficult to increase the traveling speed of the robot 101 and the cart 200.
As described above, in the conventional technique of fixedly setting the representative point of the object, there are inconveniences such as a decrease in the followability of the posture of the object to the desired posture, or an occurrence of a situation where it is difficult to increase the traveling speed of the object, according to the changing pattern of the desired posture trajectory of the object.